During formation of the visual pathway in many vertebrate embryos, the retinal ganglion cells grow from the eye onto the surfaces of the optic tectum, ultimately penetrate the tectum and form synapses. The retina projects onto the tectum with extreme precision, such that axons that originate in a particular area of the retina invariably project to a precise area of the tectum. The projection is also inverted along the dorsoventral axis such that the cells in the dorsal region of the retina project to the ventral region of the tectum, and vice versa. An in vitro attachment assay demonstrates that chick neural retinal cells (NRC) and retinal pigment epithelial cells (RPEC) can specifically recognize and attach to different areas of the surfaces of the optic tectum, thereby mimicking the projection of the retinal ganglion cells to the tecta along the dorsoventral axis. The longterm goal of this application is to understand in molecular terms the specific cell surface recognition events that must occur to allow precise formation of the retinotectal projection. The experiments in this proposal are designed to identify and characterize the cell surface factors on the NRC, RPEC, and tecta that are responsible for the specific attachment observed in the assay, 1) The biochemical properties on the specific adhesion factors will be tested using the adhesion assay by pretreating the cells with protease and glycosidases and of adding fractionated cell surface molecules. 2) Monoclonal antibodies (MAB) will be generated to intact dorsal and ventral NRC, RPEC, and tecta and screened to identify antigens present in dorsoventral concentration gradients. 3) Knowing the basic properties of the factors will allow MAB to them to be identified and then used to purify and fully characterize the factors. The effects of the antigens and antibodies to them will be tested directly on the attachment assay and in vivo during eye development and retinotectal synapse formation. The results from these experiments should provide insight into the molecular mechanisms of he specific intercellular attachments that occur during visual system development and allow a prediction of the consequences caused by a dysfunction of these attachment molecules.